The present invention relates to a device for the electrophotographic manufacture of printing forms which are stacked in the non-exposed condition in a magazine and are individually removed from the magazine by means of suction elements and transported to a loading station in order to be moved therefrom to further processing stations of the device.
Such a device is disclosed in German Offenlegungsschrift No. 3,012,815 (corresponding to U.S. Pat. No. 4,402,592). The disclosed device has a lifting cylinder which is pivotable about an axis and has a piston rod which can be extended out of and retracted into the lifting cylinder and which carries suction elements for sucking in and depositing the uppermost printing plate of the stack. The suction elements act on the uncoated side of the printing form. The suction elements for sucking in, securing and depositing the printing form onto a horizontal conveyor track are arranged on a dish-shaped plate which is connected as a holder of the suction elements to the piston rod. The conveyor track is a table, along which the printing form is transported to an exposure table arranged behind the table. The magazine is inclined to the perpendicular, with the lifting cylinder, in its receiving position, being directed perpendicularly towards the uncoated side of the uppermost printing form. The dish-shaped plate extends parallel to the uncoated side of the printing form and lowers onto the printing form until the suction elements sit on the latter for lifting the uppermost plate from the stack.
An apparatus for the electrophotographic manufacture of printing forms is described in German Patent Specification No. 2,462,216 (a divisional case of German Application No. 24 52 979.1 which corresponds to U.S. Pat. No. 4,006,984). In this apparatus, the individual printing form is lifted from a stack in a plate magazine by a transport device which consists of a transport carriage having a vacuum suction device and which transports the printing form to an exposure platform. The transport carriage runs over two guide rails and is driven by a motor which is arranged on the upper side and is in engagement with a gear having a rack-and-pinion drive which is arranged parallel to the motion direction of the transport carriage. On the underside, the transport carriage has a vacuum plate which is connected to a vacuum pump via a number of holes. When the transport carriage is placed onto the upper side of the uppermost printing plate in the plate magazine, the printing plate is sucked in towards the vacuum plate by vacuum. The transport carriage is then conveyed towards the exposure platform. The transport carriage is lowered onto the exposure platform and the printing plate is deposited onto the exposure platform by releasing the vacuum in the vacuum plate of the transport carriage. The exposure platform comprises a vacuum plate which is charged with vacuum in order to suck in the printing plate.
A device is disclosed in German Offenlegungsschrift. No. 3,012,761, corresponding to U.S. Pat. No. 4,334,472, by means of which a printing plate, which is lowered through a circular path of motion from above onto a support surface and the photoconductive, coated side of which is directed upwards, is transferred for further transport onto a device, equipped with rollers. The printing plate does not lie on the rollers and the photoconductive layer of the printing plate does not contact the rollers. For this purpose, a pivotable lifting cylinder removes the printing form, in the configuration of a printing plate, from a magazine and places the printing plate, circularly with the front part, onto a suction plate of the exposure table. A row of transport and drive rollers is, in each case, arranged parallel to the two side edges of the printing plate in the transport direction, with the transport rollers lying first in the transport direction of the printing plate being pivotable outwards out of the rows to enable the front part of the printing plate to be deposited onto the suction plate of the exposure table without jamming. Once the printing plate is deposited on the exposure table, the roller strips which are parallel to one another sit with the transport and drive rollers against the side edges of the printing plate and center the latter during exposure. Since the rollers have a certain groove depth, they project by this groove depth, in the inside of the printing plate, at the border or at the side edges of the latter, so that exposure of the printing plate towards the border is not possible.
A draw-in and transport device for printing plates is described in German Offenlegungsschrift No. 3,122,321 (which corresponds to U.S. Pat. No. 4,462,678). The device enables the printing plate to be exposed over its entire width up to the outer edges. The rollers are rotatably mounted on brackets which are fixed on two movable roller strips which are parallel to one another. Also, devices are provided to outwardly displace the roller strips parallel to the side edges of the printing plate before exposure.
The known draw-in and transport devices work mechanically and comprise either a transport carriage which secures the printing plate by vacuum and conveys the individual printing plate from processing station to processing station, or driven transport rollers which are in contact with the side edges of the printing plate to transport the latter further. These devices work satisfactorily but are of expensive mechanical construction and, their transport capacity is limited to about 60 plates per minute. A higher throughput of plates can hardly be achieved, because, as a result of the sluggishness of the mechanical parts of the transport device, putting the latter into operation and stopping it for receiving a printing plate from a table of a processing station and the transfer of an individual printing plate from processing station to processing station do not permit a higher operating frequency.